title: Mice lacking the Raf-1 kinase inhibitor protein exhibit exaggerated hypoxia-induced pulmonary hypertension.
abstract: OBJECTIVE
  Increased pulmonary vascular remodelling, pulmonary arterial pressure and pulmonary vascular resistance characterize the development of pulmonary arterial hypertension (PAH). Activation of the Raf/mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK)1/2 is thought to play an important role in PAH and Raf-1 kinase inhibitor protein (RKIP), negatively regulates this pathway. This study investigated whether genetic deletion of RKIP (and hence ERK1/2 up-regulation) resulted in a pulmonary hypertensive phenotype in mice and investigated a role for RKIP in mitogen-regulated proliferative responses in lung fibroblasts.
  
  
  METHODS
  Pulmonary vascular haemodynamics and remodelling were assessed in mice genetically deficient in RKIP (RKIP-/-) after 2 weeks of either normoxia or hypoxia. Immunoblotting and immunohistochemistry were used to examine phosphorylation of Raf-1, RKIP and ERK1/2 in mouse pulmonary arteries. In vitro, RKIP inhibition of mitogen signalling was analysed in CCL39 hamster lung fibroblasts.
  
  
  RESULTS
  RKIP-/- mice demonstrated elevated indices of PAH and ERK1/2 phosphorylation compared with wild-type (WT) mice. Hypoxic RKIP-/- mice exhibited exaggerated PAH indices. Hypoxia increased phosphorylation of Raf-1, RKIP and ERK1/2 in WT mouse pulmonary arteries and Raf-1 phosphorylation in RKIP-/- mouse pulmonary arteries. In CCL39 cells, inhibition of RKIP potentiated mitogen-induced proliferation and phosphorylation of RKIP, and Raf-1.
  
  
  CONCLUSIONS
  The lack of RKIP protein resulted in a pulmonary hypertensive phenotype, exaggerated in hypoxia. Hypoxia induced phosphorylation of RKIP signalling elements in WT pulmonary arteries. RKIP inhibition potentiated mitogen-induced proliferation in lung fibroblasts. These results provide evidence for the involvement of RKIP in suppressing the development of hypoxia-induced PAH in mice.
authors.affiliation: Institute of Cardiovascular & Medical Sciences, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, UK. ian.morecroft@glasgow.ac.uk
authors.forename: I
authors.initials: I
authors.lastname: Morecroft
authors.forename: B
authors.initials: B
authors.lastname: Doyle
authors.forename: M
authors.initials: M
authors.lastname: Nilsen
authors.forename: W
authors.initials: W
authors.lastname: Kolch
authors.forename: K
authors.initials: K
authors.lastname: Mair
authors.forename: M R
authors.initials: MR
authors.lastname: Maclean
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D049109:Cell Proliferation; D002908:Chronic Disease; D006224:Cricetinae; D003412:Cricetulus; D005347:Fibroblasts / Q000201:enzymology* / Q000473:pathology; D017353:Gene Deletion; D006976:Hypertension, Pulmonary / Q000201:enzymology / Q000209:etiology*; D000860:Hypoxia / Q000150:complications* / Q000201:enzymology; D007150:Immunohistochemistry; D008168:Lung / Q000201:enzymology* / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D019950:Mitogen-Activated Protein Kinase 1 / Q000096:biosynthesis; D049488:Phosphatidylethanolamine Binding Protein / Q000172:deficiency* / Q000235:genetics; D010766:Phosphorylation; D019908:Proto-Oncogene Proteins c-raf / Q000037:antagonists & inhibitors*; D015854:Up-Regulation
chemical_list: D049488:Phosphatidylethanolamine Binding Protein; C539308:Raf kinase inhibitory protein, mouse; D019908:Proto-Oncogene Proteins c-raf; D019950:Mitogen-Activated Protein Kinase 1